st: Michaelis-Menten and regression

I have a reasonably simple hypothesis that the form of relationship
between the independent variable (x) and the dependent variable (y)
follows the Michaelis-Menten rational function, f(x) = ax/(1+bx). I
want to have this in a regression model with the cluster() option: reg
y f(x) V, cluster(). But I can't see a way of achieving this and
having reg solve for a and b. I thought maybe a power expansion of
f(x) might work, but this does not seem appropriate.
Any thoughts greatly appreciated.
Simon Moore
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